The present invention relates to pulsed laser diodes. More specifically, but without limitation thereto, the present invention relates to driving a laser diode with a resonant electrical circuit formed by an impedance mismatch at each end of a transmission line connecting an impulse generator to the laser diode.
High energy optical pulses are widely used in applications such as optical fiber communications, optoelectronic sampling, optical clocking of logic circuits, and photonic switching. The generation of picosecond optical pulses at high pulse repetition frequencies from laser diodes has received much interest in recent years because the laser diodes are much smaller, less expensive, more reliable, and more efficient than gas lasers, and because of the variety of applications in optical signal processing and optical fiber communication systems. The majority of research in this area has centered on using active optical mode locking schemes. These schemes employ electrical modulation and utilize an optical resonant cavity, generally an external resonant cavity, although more sophisticated setups utilize a monolithic cavity structure. Passive optical mode locking schemes have also been studied. These schemes typically use a saturable absorber which results in a device that self resonates. Some of the drawbacks of these optical mode locking schemes are their complexity, and their sensitivity to mechanical vibration. Methods utilizing gain switching have also been studied. These methods have the advantage of being simple, but with the drawbacks of longer pulse width, less optical pulse power, and smaller on-off ratio than mode locking schemes.
Both mode-locking and gain-switching are commonly used to generate pulses having pulse widths in the picosecond range. The limitation on mode-locking of conventional laser diodes having a typical cavity length in the 300 .mu.m range is low pulse energy. The pulse energy of these laser diodes is approximately 1 pJ, although high energy pulses of about 50 pJ before compression were reported recently by A. Azouz et al from mode-locking a laser diode having a 2000 .mu.m cavity (A. Azouz, N. Stelmakh, P. Langlois, J-M Lourtioz, and P. Gavrilovic, "Nonlinear Chirp Compensation in High-power Broad-spectrum Pulses from Single-stripe Mode-locked Laser Diodes", IEEE Journal of Selected Topics in Quantum Electronics, vol. 1, pp. 577-582, 1995). However, mode-locking suffers from the complexity of an external cavity. Compared to mode-locking, gain-switching is simpler, more compact, and more reliable for generating high energy pulses having a duration in the range of about 10 picoseconds. Current gain-switching techniques, however, suffer the disadvantages of longer pulse widths, lower optical power, and a smaller on-off ratio than mode-locking provides. A need thus continues to exist for a circuit for driving laser diodes that combines the advantages of gain-switching and mode-locking in an inexpensive, compact, reliable laser diode circuit to produce optical pulses having a narrow pulse width, high energy, low jitter, and high extinction ratio.